A flight plan defines the route which the crew of an aircraft foresees following in order to go from its departure point to the destination point of its mission as well as the conditions for flying this route by a succession of waypoints or turn points, connected by straight or curved segments called “legs” and associated with various flight constraints of heading, altitude, speed, passage time, etc., that have to be complied with by the aircraft when it passes above them or in their vicinity. This succession of waypoints is entered into the on-board equipment of an aircraft by means of a programming interface with a keyboard and screen called an MCD or MCDU (an acronym for “Multipurpose Control and Display Unit”) and is displayed on the screens on board during the progress of the flight plan, either in graphical form, the next waypoints to come and the legs which connect them appearing superimposed on a PFD (the acronym for Primary Flight Display) primary piloting screen or on the scrolling map of a navigation screen, or in the form of a scrolling alphanumeric table listing the waypoints to come, in their order of succession on the predicted route of the flight plan with the constraints associated with each one of them, or, most often, in both the graphical and the alphanumeric forms. The chaining, by the pilot in manual piloting or by a flight management computer in automatic piloting, of the succession of waypoints predicted in the flight plan and the compliance with the specific flight constraints associated with the waypoints determine the real routing of the aircraft.
In geographic zones with dense air traffic and in the vicinity of airports, air traffic is subjected to regulations called navigation procedures, which are the subject of regular publications, and to regulation by air traffic control authorities whose instructions received during the progress of the flight take precedence over the published navigation procedures.
The published navigation procedures consist of series of “waypoints” corresponding to traffic corridors, associated with specific flight constraints. Different categories are distinguished, the principal ones of which are as follows:                navigation procedures known as SID (the acronym for “Standard Instrument Departure”) which define the paths authorized on takeoff in the proximity of an airport,        so-called “Airway” navigation procedures which define the air routes over a territory,        navigation procedure known as STAR (the acronym for “Standard Terminal Arrival Route”) which define the authorized paths when arriving at an airport,        approach procedures which define the authorized paths to the terrain of the airport (generally a landing runway).        
These navigation procedures are imposed for the terminal parts (departure, arrival and approach) of most flight plans and it is not rare for the terminal part of the predicted route in the flight plan to result from the chaining of several published navigation procedures.
During the progress of a flight, the pilot of an aircraft can be led to modify his flight plan and to change the published navigation procedure in order to comply with an instruction from an air traffic control authority. This is the case, for example, when he receives a change of landing runway instruction on approaching the destination airport. The case can arise on approaching certain large airports with parallel runways, such as Los Angeles, Atlanta, Paris CDG, London Heathrow, etc., for various reasons such as for example in order to reduce taxiing time.
For parallel runways, the approach procedures can correspond to paths that are close or even partially superimposed. At Los Angeles, the approach procedures have “waypoints” with different names whilst this is not the case for certain approach procedures at Heathrow.
When an air traffic control authority asks an aircraft to change its landing runway, the pilot will search in a navigation database for the published navigation procedure or procedures appropriate for the approach to the new runway in order to substitute them for those that are no longer suitable and initially appearing in the flight plan programmed in the on-board equipment of the aircraft.
This operation can have undesirable effects insofar as it provokes a reiteration of the operation of chaining published navigation procedures over the terminal part of the route predicted in the flight plan. Indeed, it is possible that the new navigation procedures adopted partially reuse published navigation procedures adopted in the initial flight plan but having been modified by the pilot during the progress of the flight in order to comply with one or more instructions from an air traffic control authority. Given the sharing of airspace in zones of competence, these modifications diverging from the published regulations can be unknown to the air traffic control authority asking for the change of landing runway and which therefore has no reason to recall them. Not being reiterated to the crew of the aircraft, there is a risk that they are not taken into account when there is a change of approach procedure. Thus, an altitude constraint, imposed by an air traffic control authority on passing a “waypoint” forming part of the initial approach procedure not recalled by the control authority asking for the change of landing runway whereas the “waypoint” is still part of the new approach procedure, runs a certain risk of not being complied with out informing the crew.
These problems exist with no matter what change of terminal procedure (departure, arrival, approach) as soon as any modification whatsoever has been made (constraint, adding of intermediate waypoints) and which applies to a portion common to the old procedure and to the new procedure.
In order to deal with this, it is known to retain the inactivated old navigation procedure or procedures in the alphanumeric table for displaying the route of a flight plan. This technique is little appreciated because it amounts to causing the same waypoints to appear several times in an alphanumeric table of the flight plan, or even to cause whole sequences of waypoints which will not be flown to appear in this table and to oblige the crew to differentiate between the active and inactive waypoints when it is monitoring the correct progress of the flight plan, which increases its workload during difficult phases such as an approach flight phase.